INTRO: All marine mammals have the remarkable ability to dive and forage for extended periods below the ocean surface. But few marine mammals dive deeper or stay longer below the surface than do elephant seals. As Doug Schneider reports in this week's Arctic Science Journeys Radio, one Alaska scientist is unraveling the mysteries of the elephant seal's amazing diving ability.

STORY: Alaska is famous for its walrus,
its seals and its Steller sea lions. But few
people know that Alaska plays host to thousands
of northern elephant seals, too. That's probably
because elephant seals don't usually come
ashore in Alaska. And they don't spend much
time lounging about on the surface, either,
so few people ever catch a glimpse. Rather,
they spend the summer foraging the deep ocean
seafloor—usually from 1,000 to 2,500
feet below the surface, but sometimes as deep
as 5,000 feet. Exactly how these two-tonned
hulks are able to dive to depths that would
crush other animals is a mystery that scientist
Russ Andrews is trying to unravel.

ANDREWS: "You can imagine that it's
really difficult to go to those really great
depths. So we know their bodies are put together
to allow them to be squeezed. I'm sure
that even if you just swim to the bottom of
the pool, you sense your ears starting to
squeeze. And if you're a scuba diver,
you know that your sinuses really start to
hurt. The same thing happens in your lungs
because your lungs are not made to be squished
by that high pressure. And if they can't
squish because of the physical structure,
like the way we're put together, blood
has to fill that space. And that means blood
is coming out of blood vessels—that shouldn't
happen. This doesn't happen in marine
mammals, and especially elephant seals because
they are put together differently to be able
to handle going down really deep."

Russ Andrews is a marine biologist at the
Alaska SeaLife Center in Seward, Alaska, and
a research professor at the University of
Alaska Fairbanks School of Fisheries and Ocean
Sciences. He's spent years studying elephant
seals, and he says this unusual marine mammal
has physiologically evolved into an amazing
diving machine.

ANDREWS: "They are sort of prepared to leave
the surface because they have built up a lot
of oxygen storage. They breathe really fast
so they store up a lot of oxygen. Surprisingly
they don't do what we do—take a really
big deep breath as our last breath and go
down. Well they don't do that. They have so
much ability to store oxygen in their blood
that they actually exhale on their very last
breath. By exhaling, that means there's less
air in their lungs, and it's easier for their
lungs to collapse. So as they start to swim
down, the first thing they do is slow their
heart rate. So it can cut off blood flow to
parts of its body to slow down how fast its
overall body is using that oxygen that's now
only stored up inside them. Then they start
to dive down. As they're diving down their
lungs are getting squeezed more and more and
more. That means they're getting more and
more negatively buoyant. So they sink. And
after a while they don't even have to use
their flippers anymore to push them down.
They can just start gliding down. It'd be
like you and I having a whole bunch of lead
weights. We'd just fall to the bottom."

Elephant
seals have a unique ability to store large
amounts of oxygen in their blood. All
that oxygen comes in handy during deep
dives. (Courtesy Russ Andrews, Alaska
SeaLife Center.) Click image to see
larger version.

Throughout the descent, the heart rate continues
to decline. In some seals the heart rate slows
to just three beats per minute. Once on the
bottom, however, their heart rate increases
as they swim about to find food. Elephant
seals typically stay underwater for about
30 minutes, but scientists have monitored
individuals that stayed below the surface
for two hours.

Russ Andrews says elephant seals dive almost
constantly, even when they're just traveling
from place to place. Going to the surface
just long enough to get air is probably an
adaptation aimed at avoiding surface predators
like sharks and killer whales.

ANDREWS: "There are some elephant seals that
never spent more than 10 minutes at the surface
at any one time. A few elephant seals had
extended surface intervals of maybe one or
two hours at the surface at a time. But this
is one or two hours out of five or six or
seven months at sea."

Elephant
seals are diving machines. They spend
very little time resting at the surface.
(Courtesy Russ Andrews, Alaska SeaLife
Center.) Click image to see larger
version.

And since elephant seals seem always to be
diving, Andrews wondered when they would have
time to sleep. And while he hasn't yet
proved it, he thinks elephant seals have evolved
a unique solution.

ANDREWS: "If they are indeed gliding
on the way down, that means they can probably
go to sleep, too. And so that's what
we want to look at next."

Whether elephant seals actually sleep during
their dives is a question he hopes to solve
by monitoring the brain waves of several seals
during their descents. If it's true that
seals actually sleep while sinking to the
seafloor, Andrews will have even more questions.

ANDREWS: "That raises the question of
what keeps them from gliding into the abyss
of the ocean? Even though they're built
for being squeezed by pressure, they aren't
perfect. They need something to wake them
up and keep them from going too deep. There's
some tricks there we don't understand."

OUTRO: This is Arctic Science Journeys
Radio, a production of the Alaska Sea Grant
Program and the University of Alaska Fairbanks.
I'm Doug Schneider.

Arctic Science Journeys is a radio service highlighting science,
culture, and the environment of the circumpolar north. Produced by the
Alaska Sea Grant College Program and the University of Alaska Fairbanks.
The shortcut to our ASJ news home page is www.asjnews.org.

While
a rare event, northern elephant seals sometimes
haul out onto Alaska shores. In March 1999,
a juvenile elephant seal hauled out just down
the street from the Alaska SeaLife Center
in Seward, Alaska. It was brought to the center
for rehabilitation because it was suffering
from a disease called "scabby molt." This
elephant seal was released back into the wild
a few months later.

Some
200,000 northern elephant seals roam the waters
of the Gulf of Alaska, during months-long
feeding migrations from breeding grounds off
California.